In today's increasingly electronic world, we say our personality traits are "hard-wired" and we "replay" our memories. But we use a different metaphor when we speak of someone "reading" another's mind or a desire to "turn over a new leaf" - these phrases refer to the "book of the self", an idea that dates from the beginnings of Western culture. Eric Jager traces the history and psychology of the self-as-text concept from antiquity to the modern day.

He focuses especially on the Middle Ages, when the metaphor of a "book of the heart" modelled on the manuscript codex attained its most vivid expressions in literature and art. For instance, mediaeval saints' legends tell of martyrs whose hearts recorded divine inscriptions; lyrics and romances feature lovers whose hearts are inscribed with their passion; paintings depict hearts as books; and mediaeval scribes even produced manuscript codices shaped like hearts. In a far-reaching conclusion, Jager considers what the much-prophesied "death of the book" might portend for 21st-century conceptions of the post-textual self.